In its latest quarterly report, the WPIC increased its forecast surplus for 2018 from 295,000oz to 505,000oz, citing weaker demand for platinum jewellery.
It had originally estimated a deficit for 2018 but changed its outlook for a move into surplus for the first time in five years in its June report.
"2018 is proving to be a tough year for platinum as our Q3 report shows, especially as the automotive sector remains subdued," WPIC CEO Paul Wilson said.
"However, we believe we can look forward to a number of promising trends in 2019."
The report expected the 2019 surplus would be 10% lower at 455,000oz, due to a 1.6% increase in supply and a 2.4% increase in demand, driven by chemical and petroleum demand and a doubling in investment demand.
"We believe more ETF investors find platinum's widening price discount to palladium and rhodium interesting," Wilson said.
The palladium price has seen a growing premium to platinum over the past year, hitting an all-time high earlier this month.
"Beyond the 2019 forecast, we see Platinum Group Metal (PGM) substitution in platinum's favour and platinum investment growth as key drivers," the report stated.
The Bloomberg chart below illustrates the growing divergence between the platinum and palladium (red line) spot prices over the past year.